f you hire a money manager who invests in low-cost index funds that track the stock and bond market averages, take a close look at the index funds he or she uses.

The average stock mutual fund sports expenses of 1.4 percent annually. But index funds offered by Dimensional Fund Advisors (DFA) and Vanguard Group are two-thirds less expensive.

This means more of your money is invested over the long term.

We've frequently touted Vanguard index funds, which have the reputation of being among the lowest cost. The less you pay, the more you stand to earn.

Dimensional Fund Advisors is not as widely available. That's because they're strictly for institutional investors and clients of registered financial advisors.

Both investment companies offer a wide variety of mutual funds at low cost.

But Paul Merriman, a Seattle-based money manager and publisher of FundAdvice.com, believes that Dimensional Fund Advisor's index funds, if you can find them, are the better deal.

Dimensional Fund Advisors index funds tend to invest more heavily in small and undervalued companies. Financial research reveals that these outperform large growth-oriented companies over the long term, he says.

The fund group also has slightly lower expenses than Vanguard. Plus, it offers more of a selection of index funds for asset allocation.

"(Dimensional Fund Advisor's) edge comes not from stock selection but from precise asset allocation that gives investors more of what they need and less of what they don't need," Merriman says.

Merriman says investors need diversification in addition to large company growth stocks.

"The stronger the orientation to value, the better," he says, "and the smaller the companies are the better."

Be advised: If you hire someone to manage of portfolio of Dimensional's funds, you typically pay the investment advisor an annual fee of at least 1 percent of assets. By contrast, you can manage your own money at Vanguard and save the annual investment advisor charge.

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Spouses Gail Liberman and Alan Lavine are syndicated columnists. Their latest book is "Rags to Retirement (Alpha Books)." You can e-mail them at MWliblav@aol.com.